Field
The present invention relates to a semiconductor device and a method of fabricating the same, and more particularly, to a semiconductor device having an insulation structure for insulating a semiconductor stack from a substrate and a method of fabricating the same.
Discussion of the Background
Gallium nitride compound semiconductors may be used in visible or ultraviolet (UV) light emitting devices, high power electronic devices, and the like. A gallium nitride compound semiconductor layer is generally grown on a substrate by a growth technique such as molecular beam epitaxy (MBE), metal-organic chemical vapor deposition (MOCVD) or hydride vapor phase epitaxy (HVPE).
Generally, a gallium nitride compound semiconductor may be grown on a heterogeneous substrate such as a sapphire substrate. When a semiconductor stack is grown on the sapphire substrate, various semiconductor devices may be fabricated using the semiconductor stack.
Recently, a light emitting device may be fabricated by connecting a plurality of semiconductor stacks to each other in series via an interconnection wire on a single substrate for high voltage operation. Such a light emitting device may be formed using an insulating substrate such as a sapphire substrate as a growth substrate. Thus, electric isolation between the semiconductor stacks may be relatively easily achieved by patterning semiconductor layers grown on the growth substrate such that the substrate can be exposed therethrough.
However, a semiconductor stack grown on a sapphire substrate may have a relatively high crystal defect density. Moreover, a gallium nitride compound semiconductor grown in a C-axis direction on a sapphire substrate having a c-plane as a growth plane may exhibit polarity by spontaneous polarization and piezoelectric polarization, and provide low recombination rate between holes and electrons, thereby limiting improvement in luminous efficacy.
Recently, in order to overcome such problems of the sapphire substrate, a technique of growing a gallium nitride compound semiconductor using a gallium nitride substrate as a growth substrate has been developed. In this case, since a homogeneous substrate, that is, the gallium nitride substrate, is used as the growth substrate, it is possible to achieve significant reduction in crystal defect density. Furthermore, when a non-polar or semi-polar gallium nitride substrate is used as the growth substrate, a non-polar or semi-polar gallium nitride compound semiconductor may be grown to have good crystallinity, thereby solving problems caused by polarization.
However, the gallium nitride substrate has electrical conductivity, unlike the sapphire substrate. Even when a relatively high resistance gallium nitride substrate is fabricated, the gallium nitride substrate may be much thicker than a semiconductor stack, so that substantial current leakage occurs through the gallium nitride substrate. Accordingly, in order to connect a plurality of semiconductor stacks to each other in series on an electrically conductivity-substrate such as a gallium nitride substrate, it is necessary to insulate the plurality of semiconductor stacks from the substrate.
In order to insulate the gallium nitride substrate from the semiconductor stack, a gallium nitride semi-insulation layer formed by counter doping of a p-type impurity may be used. However, counter doping of the p-type impurity may have a limit in formation of a uniform insulation layer. Moreover, since the semi-insulation layer may not provide complete blocking of electric current, current leakage may easily occur through the semi-insulation layer.
On the other hand, when a plurality of semiconductor chips grown on a gallium nitride substrate is mounted on a printed substrate or the like, electrical conductivity of the gallium nitride substrate may result in a short circuit between the semiconductor chips due to current leakage through the gallium nitride substrate.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form any part of the prior art nor what the prior art may suggest to a person of ordinary skill in the art.